1. Field of the Invention
The present invention relates to a projection display device such as a projector etc., and more specifically to a projection display device for displaying an image by projecting the image on the screen etc. using a display device.
2. Description of the Related Art
Conventionally, a lamp light source such as an extra high pressure mercury lamp etc. has been used as a light source of a projection display device using a display device. Since such a lamplight source is short-life, a maintenance operation such as exchanging a lamp is frequently performed. In addition, when color images are displayed, it is necessary to provide, for example, an optical system for taking out red light, green light, and blue light from white light emitted from a lamp light source. Therefore, the device configuration is complicated and the light use efficiency is reduced.
On the other hand, although a projection display device using an LED light source has been proposed as a light source, it is low in the light use efficiency of the LED, thereby failing in attaining sufficient luminance on the displayed image.
Therefore, there has been an attempt to use a laser light source such as a semiconductor laser etc. as a light source of a projection display device. Since the laser light source is longer-life than the lamp light source, maintaining operations are not required substantially. In addition, since laser light can be directly modulated depending on a displayed image when the laser light source is used, the device configuration is simple and the light use efficiency can be improved. Furthermore, using a laser light source, a larger color reproduction area can be obtained.
However, a laser light source has high coherence. Therefore, when a laser light source is used as a light source of a projection display device, a pattern of high-contrast spots such as a speckle, speckle noise, speckle patterns, etc. (hereinafter also referred to simply as “speckle”) is formed on the screen, thereby degrading the quality of displayed images. Therefore, when a laser light source is used as a light source, it is important to reduce the speckle. Accordingly, the technology of reducing the speckle has been proposed in the following variations.
FIG. 1 is a configuration of the optical system of the projection display device disclosed by the patent document 1 (Japanese Laid-open Patent Publication No. 2008-268271). A projection display device 101 illustrated in FIG. 1 includes a laser light source 102, an optical system for illumination 103, a reflective optical modulation element 104, and an optical system for projection 105. The laser light source 102 emits coherent light. The optical system for illumination 103 propagates the luminous flux emitted from the laser light source 102 into a predetermined optical path, and leads the flux to the screen side. The reflective optical modulation element 104 forms on an illuminated surface 104a illuminated by the luminous flux lead by the optical system for illumination 103 an image to be displayed on the screen. The optical system for projection 105 scales up and projects on the screen the image formed on the illuminated surface 104a of the reflective optical modulation element 104. In the optical system for illumination 103, the speckle can be reduced by providing near a stop position 106 of the optical system for illumination 103 a diffusion element 107 for diffusing the luminous flux emitted from the laser light source 102.
FIG. 2 is a perspective view of the outline of the configuration of the illumination device disclosed by the patent document 2 (Japanese Laid-open Patent Publication No. 2007-33577). An illumination device 111 illustrated in FIG. 2 includes an optical system for conversion 112 for converging a plurality of received beams of laser light L1, and a diffusion optical element 113 for diffusing the light converged by the optical system for conversion 112 and generating diffusion light L2. The speckle can be reduced by illuminating a first surface 114 by the diffusion light L2.
FIG. 3 illustrates the outline of the configuration of the laser light source device disclosed by the patent document 3 (Japanese Laid-open Patent Publication No. 2008-96777). A laser light source device 121 illustrated in FIG. 3 includes a laser light source 122 having a plurality of emission points for emitting laser light, a converging lens 123 for converging the laser light emitted from the plurality of emission points, and a diffusion element 124, provided near the converging point of the laser light, having a hologram for expanding the diffusion angle of the laser light. The speckle can be reduced by the diffusion element 124 having a diffusing operation of expanding the diffusion angle of each beam of the laser light so that two or more beams of the plurality of beams of the laser light can overlap each other.
FIG. 4 illustrates the outline of the configuration of the projector disclosed by the patent document 4 (Japanese Laid-open Patent Publication No. 2007-279204). A projector 131 includes liquid crystal spatial light modulators 133R, 133G, and 133B, a diffusion unit 134, and an optical system for projection 135. The liquid crystal spatial light modulators 133R, 133G, and 133B are image forming units for forming images using the light from the light source units 132R, 132G, and 132B having a solid state light source, respectively. The diffusion unit 134 is provided in the image forming position of the image formed by the image forming unit, and diffuses light. The optical system for projection 135 projects the light from the diffusion unit 134. The speckle can be reduced by the diffusion unit 134 changing the phase of the light at random for each position where light enters. An optical system for forming images 136 forms an image of a liquid crystal spatial light modulator by the diffusion unit 134.